The present invention relates to the use of closely spaced video screen systems sometimes known as a video wall and which enables the construction of a wide variety of configurable cells in a closely spaced relationship in an inexpensive manner but without the distorting effects from thermal and moisture cycling.
Video screens are typically made from polymethyl methacrylate, or acrylic. Single unit systems such as are used in big screen video projection systems usually do not present a problem especially where the screen can be suspended using force members on a frame. However, in custom installations of multiple screens, the object is to achieve high density in multiple screen structures, typically in some configuration of a xe2x80x9cwallxe2x80x9d or continuous planar array of such screens. Where extremely close spacing is required or desired, the availability to add tensioning structures is eliminated.
In conventional vide wall video screen projection systems, a frame work is made of steel or aluminum. Since the thermal expansion coefficient of acrylic, about 34xc3x9710xe2x88x926 inch/inch/xc2x0 F., is about two to three times greater than the expansion coefficient for either steel, from about 8.4xc3x9710xe2x88x926 inch/inch/xc2x0 F. to about 15xc3x9710xe2x88x926 inch/inch/xc2x0 F., or aluminum, from about 9xc3x9710xe2x88x926 inch/inch/xc2x0 F. to about 13xc3x9710xe2x88x926 inch/inch/xc2x0 F., differential expansion an contraction will occur. The differential expansion and contraction will create screen distortion if the cut and fit sizing of the screens in the frames was performed under different thermal conditions than the operating conditions. While all screen system are subject to fluctuating ambient conditions, screen distortion will occur if the screen(s) expand in a fixed frame if the frame itself cannot expand.
Further, acrylic is hygroscopic and expands with increased humidity regardless of temperature. Humidity conditions can produce a marked differential expansion of the acrylic material with respect to steel and aluminum which are unaffected. Both of these effects cannot be compensated for unless absolute humidity and temperature is maintained from the time the screen frame structure is constructed and the acrylic is cut to fit the individual cell structure and throughout the operable life of the assembled screen structure. This requirement is not achievable, even where desired, due to high operating cost and the probability of heating, ventilation and air conditioning failure and power failures.
In general, the distortions are caused by making the acrylic screen large enough such that expansion may impinge the frame and cause the plane of the acrylic screen to bend out of plane, either inward or outward, a process known as xe2x80x9coil canningxe2x80x9d. Movement of part of the acrylic screen out of its plane causes a de-focussing of the video projected image. On the other hand, where the acrylic video screens are cut smaller than the frame sizes, a shrinking of the acrylic screen with respect to its steel or aluminum frame can cause the creation of a gap between the edge of the acrylic screen and the metal frame. At best, an unacceptable light gap occurs and the project light is glaringly directed at the eyes of the viewer. At worse, the edge of the screen may be displaced forward or rearward to combine glare with a partially out of focus screen.
One solution to the expansion problem has been the use of a polycarbonate sheet as an intermediate attachment member between the screen and frame. Adjoining screens have a separation of from one and a half to two millimeters to allow expansion and contraction of the screens to operate within the gap, with each screen presumably occupying half of the space assuming both expand and contract at the same time.
In another solution, screens are cut to exact size and holes drilled about the periphery of the screens. The screens are then literally stitched, during the on-site construction activity, with xe2x80x9cUxe2x80x9d shaped steel wires to a flexible steel frame. The flexible steel is mounted to the substantial metal framework. The labor required in this system is tremendously greater than in other systems, and the three body system utilizes the flexible metal strip for expansion and contraction.
To meet the above described need, a system for suspending a video projection screen includes the principles of physical independence, or a somewhat xe2x80x9cfloating system,xe2x80x9d employing at least some thermal expansion matching, centroid expansion dimension splitting combined with front to back progressive dimensional freedom, as well as corner gussets and rear corner brackets which contribute to the overall independence of each element of the system. The system of support provide clearance space from the rear of the system and which progressively provides a final touching clearance at the projection end of the system which has the minimum spacing between adjacent acrylic members to provide a nearly seamless system.
In one embodiment, an expanse of typical acrylic screen material which may be either case, such as a Fresnel, or lenticular-fresnel material, or extruded, such as a diffusion material, having a thermal expansion of about 34xc3x9710xe2x88x926 inch/inch/xc2x0 F. A polycarbonate strip of material is attached to the four edges of the acrylic screen, and to an extruded polycarbonate frame, preferably black and preferably having a thermal expansion coefficient substantially similar to that of the acrylic screen material, the polycarbonate screen having a thermal expansion coefficient such as about 38xc3x9710xe2x88x926 inch/inch/xc2x0 F. Thus, only the example given, the thermal expansion coefficient of the frame will differ from the thermal expansion coefficient of the screen by about twelve percent. Preferably the expansion coefficient of the frame will not differ from the thermal expansion coefficient of the screen by more than about thirty percent in order to remain substantially similar. A space is maintained between the rear face of the acrylic screen expanse and the rigid extruded framework of aluminum or steel. The gap is made opaque by a black masking material.
The construction of the invention allows the frame to expand and contract substantially in unison with the screen, thus keeping the screen flat and the projected video image in focus.